Problems related to water and salt balance are frequent in the newborn. In particular, the preterm neonate with the respiratory distress syndrome is prone to intrathoracic and central nervous system complications that may involve altered antidiuretic hormone (ADH) dynamics. We propose to examine urinary excretion of ADH - a reflection of neurohypophyseal release - and urinary excretion of ADH-neurophysin, in the normal neonate and in the preterm neonate at different gestational and postnatal ages. We will compare the normal dynamics with ADH and ADH-neurophysin excretion in neonates with conditions where ADH may play a role in pathogenesis, and we will examine the value of these assays in the prevention and management of these conditions. In addition, we will measure ADH and ADH-neurophysin concentrations in amniotic fluid obtained for diagnostic purposes at different gestational ages. We will correlate these concentrations with maternal urinary ADH and ADH-neurophysin excretion, with cord blood concentrations and with gestational age, fetal diagnosis and outcome of the pregnancy. To perform these measurements, we have developed highly sensitive and specific radioimmunoassays that permit us to measure not only ADH and its specific neurophysin in different biological specimens, but other hypothalamo-neurohypophyseal principles as well (oxytocin-neurophysin, vasotocin).